Gallery: Nik Wallenda challenges Niagara Falls

Nik Wallenda, 33, walks a tightrope across Niagara Falls, from the U.S. side to the Canadian one, on Friday, June 15, 2012. Thousands of people are watching at the falls, while several billions are expected to watch him on TV. Wallenda will wear a safety harness at the insistence of ABC television, which is broadcasting the event. He is a seventh-generation member of the celebrated circus family Flying Wallendas.